The use of endoprostheses such as stents, stent-grafts and grafts is well known in maintaining the patency of bodily vessels including blood vessels and biliary ducts. When the term ‘stent’ is used herein, it is to be understood in a general sense as including all such expandable prostheses, unless otherwise indicated. Typically, a stent is implanted in a vessel which has been occluded, which is subject to an aneurysm, which has a lesion present or is otherwise damaged. Often, during the implantation of the stent, the vessel will suffer from trauma. The trauma may be as a result of the dilation prior to the implantation of the stent, the presence of a foreign body (the stent) in the bodily vessel or as a result of other causes. Although it is desirable to maintain the vessel at as large a diameter as possible to minimize the possibility of restenosis, the weakening of the vessel resulting from trauma may limit the extent to which the vessel can be dilated.
The endoprostheses that are currently available include mechanically expandable stents such as balloon expandable stents, and self-expanding devices. Mechanically expandable stents are typically expanded to a desired diameter by a radially outward force to the stent with an expansion device such as a balloon. Balloon expanded stents typically are incapable of further expansion unless a balloon is reinserted in the stent and expanded. Self-expanding stents are typically made of a shape memory material or a resilient material such as spring steel. The stent is typically constrained by a sheath or other containing device which adds to the profile of the delivery catheter. Upon removal of the sheath the stent self-expands. Self-expanding stents continually exert an outward force as they try to attain their maximum possible diameter stent as well as aspects of a self-expanding stent are known. An example of a hybrid stent is described in U.S. Pat. No. 6,168,621 B1 to Vrba. Self-expanding stents which are temporarily restrained from self-expanding are also known. An example of a self-expanding stent which is restrained from, self-expanding by a coating is disclosed in U.S. Pat. No. 5,899,935. An example of a stent which is restrained from self-expanding by restraining bands which are constructed to fail is disclosed in WO 00/41649.
It would be desirable to provide an endoprosthesis which has some of the characteristics of balloon expandable stents prior to deployment thereby allowing the stent to be useable with a relatively low profile balloon catheter, but which is also capable of self-expanding following an initial balloon expansion of the stent. It is further desirable to provide an endoprosthesis which is temporarily restrained from self-expanding, which does not rely on the use of a coating for such a restraint. It is also desirable to provide an endoprosthesis requiring a force in excess of that which the endoprosthesis experiences in the body in order to break the restraining members.
The entire content of all US and foreign patents, patent applications and publications listed herein are incorporated herein by reference.
The invention in various of its embodiment is summarized below. Additional details of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.